Above 12,200 m (40,000 ft), 100 percent oxygen must be breathed with additional pressure to achieve adequate oxygenation to prevent hypoxia. This is termed Positive Pressure Breathing (PPB). The level of positive pressure is generated by the O2 device as a function of the altitude level required to maintain PAO2 at the minimal value that will allow a pilot to perform flight-saving procedures within a few minutes. In other words, positive pressure is equal to the difference between the environmental barometric pressure and the needed lung pressure (196 hPa) allowing PAO2 to be kept at 80 hPa.

5.3 Technique for pressure breathing
During PPB, breathing patterns are inverted as inspiration becomes passive and easy and expiration becomes active and difficult. As a result, breathing must be consciously controlled to avoid hyperventilation. Practice is required to become accustomed to this reversed breathing pattern.
The best technique for PPB is as follows:

• Establish mental discipline to control breathing
• When inhaling, maintain a conscious tension of the respiratory muscles (diaphragm and abdominal muscles). Control the expansion of the thorax through muscle tension. As inhalation progresses, steadily decrease muscle tension to allow progressive lung inflation
• Pause when the desired lung inflation has occurred
• When ready to exhale, positively increase muscle tension for a steady, smooth exhalation
• Pause and breathe at a rate slower than normal

And even having this pounded into my thick skull several times in class, when the time came for actual practice in the chamber, I immediately suspected the exhaust valve in my mask had failed.

I think your scenario is quite plausible. Diabolical, but plausible.

The information seems to be pointing towards something intentional, but why assume it would be from one or both pilots? I don't really want to expand, but it seems very obvious that there are as many options as there are people on board, especially in the context of more relaxed access to the cockpit.

Or is the F/O's "Kim Jong-Un" haircut a giveaway?

There certainly are many options... what intrigues me is how they knew to go NORDO with the hand off to vietnam control. That makes it trend toward one of the pilots, though of course not conclusively. Every answer leads to 500 more questions...

I just read that the last satellite ping was about 1000 miles off the west coast of Austrailia.

Wild stuff here. Sounds like this might be one of a kind.

You can "spin it up" to FL500.

A single pilot going nuts, with 238 people not willing to go along, requires some sort of of Silk Air scenario, where you bring the flight down before people can react, in such a violent way they can't react.

In my mind, to keep the crowd controlled, or guessing wrong, you almost certainly have to have several people involved. And you have multiple people involved, you have training and coordination. You know to turn off the txpndr, and not talk about it on the radio. Basic. So there nothing I see that requires one of the pilots to participate, vs. any bad guy being introduced into the cockpit after the pilots are neutralized.

No pilot helped turn over an airplane on 9/11. Maybe this time is different, maybe it isn't.

Sink, I think the evidence now points to one of the pilots going crazy.

Rick, since we're considering the scenario of a carefully planned event by someone who knew the aircraft well, the perpetrator could have disarmed the automatic deployment of the O2 masks by pulling the cb and used the direct manual control of the outflow valves to dump the pressure quickly.

Also, even if the masks dropped they would only provide 15 minutes or so and they would be confined to their seats. I'm gonna call this scenario "plausible".

First.... I can't take much more of Wolf Blitzer. He's gotta go. Painful to listen to his "expertise".

Second.... How about an out of control avionics or electrical fire at altitude? Improper maintenance or something leads to a fire that takes out an essential bus that has the primary radios and transponder on it (or they quickly start pulling circuit breakers when smoke or flames enter cockpit), they make a turn to try to divert but are overcome by smoke or fire which takes out passengers as well. The San Fran crash shows the 777 can take a lot of damage but stay together for a while (perhaps while on fire). Fire burns itself out as they climb or run out of oxygen (or maybe it just keeps smoldering/burning) but plane keeps flying off autopilot and makes the altitude changes shown as it flounders around until it just runs out if gas or belly lands intact into the ocean and eventually sinks with no ELT going off.

Thoughts? Just an option that doesn't involve suicide,terrorism, aliens, or another season of Lost.